In order to take substantially maximum output from a permanent magnet type electric power generator connected to a windmill or waterwheel by converting alternating current to direct current without using a PWM (Pulse Width Modulation) converter, the applicant of the present application had proposed an electric power generating apparatus for dispersed power supply comprising a permanent magnet type electric power generator including a plurality of windings producing different induced voltages, respectively, and having output terminals each connected in series through a reactor to a rectifier, and the direct current outputs of these rectifiers being connected in parallel to one another, thereby outputting the direct current to the external (refer to, for example, Patent Literature 1, Japanese Patent Application 2002-221,714, FIG. 1).
Such an apparatus of the prior art will be explained with reference to a single-line diagram of the main circuit illustrating a small size wind power generating apparatus connected to a windmill shown in FIG. 9.
In FIG. 9, a windmill is denoted by reference numeral 1 and the small size wind power generating apparatus of the prior art is denoted by numeral 2 comprising a permanent magnet type electric power generator 3, first to third reactors 4 to 6, first to third rectifiers 7 to 9, a positive output terminal 10, and a negative output terminal 11, and a battery 12.
The permanent magnet type electric power generator 3 includes three windings insulated and different in induced voltage. The first winding W1 among them produces the lowest induced voltage because of the least number of turns and is connected to the first reactor 4 and further to the first rectifier 7. The second winding W2 whose number of the turns is larger than that of the first winding W1 but less than the third winding W3 is connected to the second reactor 5 and further to the second rectifier 8.
The third winding W3 produces the highest induced voltage because of the largest number of turns and is connected to the third reactor 6 and further to the third rectifier 9.
The direct current outputs of each of the first to third rectifiers 7 to 9 are connected to the positive output terminal 10 and the negative output terminal 11 in parallel respectively, and the total output of the respective windings is input to the battery 12.
A method for obtaining the substantially maximum output from the windmill by means of the electric power generating apparatus 2 for dispersed power supply thus configured will be described hereinafter.
FIG. 8 is a diagram for explaining the outline of the number of revolutions of the windmill to output characteristic when wind speed is a parameter.
With a windmill, if the shape of the windmill and wind speed U are determined, the output P of the windmill is primarily determined with respect to the number of revolutions N of the windmill. For example, the outputs P of the windmill for the wind speeds UX and UY are illustrated in solid lines in FIG. 8, respectively. Peak values of the outputs P of the windmill for various wind speeds are shown in a dot-and-dash line as a maximum output curve in FIG. 8.
In more detail, with the number of revolutions of the windmill to output characteristic in FIG. 8, when the wind speed is UX, the maximum output PX of the windmill is obtained at the number of revolutions NX of the windmill as shown at the intersection point SX of the windmill output curve with the maximum output curve.
Moreover, when the wind speed is UY, the maximum output PY of the windmill is obtained at the number of revolutions NY of the windmill.
Namely, when viewed the maximum output curve in FIG. 8 from another standpoint, this curve indicates the fact that in order to obtain the maximum output from the wind, upon the number of revolutions N of the windmill being determined, the maximum output can be obtained by primarily determining the output P of the permanent magnet type electric power generator at a value on the maximum output curve.
FIG. 7 is an explanatory view when the direct current outputs of the small size wind power generating apparatus 2 of the prior art are connected to a constant-voltage power supply such as a battery or the like. As shown in FIG. 7, respective outputs of the first to third windings W1 to W3 in the permanent magnet type electric power generator 3 of the small size wind power generating apparatus 2 are shown as the number of revolutions of windmill to output characteristic curves P1 to P3 for the respective windings in FIG. 7, owing to difference in induced voltages of the windings and voltage drops caused by internal inductances of the respective windings and the reactors connected to the outputs of the respective windings.
In other words, when the number of revolutions N of the windmill is low, the battery is not charged because the produced voltage V3 of the third winding W3 is lower than the battery voltage Vb. However, when the number of revolutions N of the windmill increases to a value near to N3, the electric current starts to flow. When the number of revolutions N of the windmill attains N3, the output P3 of the third winding W3 becomes P31. Even if the number of revolutions N of the windmill increases so as to exceed N3 to increase the induced voltage, the voltage Vb of the battery will remain at substantially constant value so that the output P3 remains at a slightly higher value than P31, because the impedance owing to inductances and other effect of the third winding W3 and the third reactor is proportional to the frequency.
With the second winding W2, the induced voltage is raised with a further increase in number of revolutions N to start obtaining the output which is large output because the internal inductance and the like may be small. With the first winding W1, even larger output can be obtained when the number of revolutions N is further increased.
With the small size wind power generating apparatus 2 thus constructed, the output to the constant-voltage power supply such as the battery 12 or the like is equal to the total output obtained by summing up the outputs P1 to P3 of the first to third windings and illustrated by approximate output curves as shown in broken lines in FIG. 6. As shown in FIG. 6, therefore, this total output realizes approximate output curves relative to the maximum output curve shown in a solid line in FIG. 6.